The teacher, along with his students, _____ on the ground in the setting sun. [ ]

A. play

B. playing

C. is playing

D. are playing

广播通讯要在有限的播出时间里表现更丰富的内容，适应听众“听”的需要，尤其需要精选和精用（ ）

A．主题

B．材料

C．结构

D．概念